We present results for the comparison of three methods of NRR of
the set of original images described above, one based on pairwise
registration to a reference image, the others two variants of a
groupwise algorithm, based on minimising description length [2].

2#2

The plots below show that, whatever number of modes (active dimensions) are
retained in the model, the two groupwise approaches are better
than the pairwise approach, but were not distinguishable from each
other.